Going Beyond the Basic Pressure Ratings: In-depth Analysis of Utilizing ASME B16.34 P-T Ratings for API 602/BS 1873 Globe Valves

I. Key Points of ASME B16.34 P-T Ratings

1. Classification of Pressure Ratings

2. Impact of Temperature on Pressure Ratings

ASME B16.34 emphasizes the impact of temperature on the pressure ratings of valves. As the temperature rises, the strength of materials will decrease. Therefore, in high-temperature working conditions, the actual working pressure of the valve needs to be reduced accordingly. For example, a Class 150 valve can withstand relatively high pressure at room temperature, but its maximum allowable working pressure will drop significantly at high temperatures.

3. Importance of Test Pressure

In addition to the working pressure, ASME B16.34 also stipulates the test pressure of valves. The test pressure is usually 1.5 times the working pressure and is used to ensure the safety and reliability of the valve in actual use. For example, for a Class 300 valve, the maximum allowable working pressure at room temperature is 5.0 MPa, and its shell hydrostatic test pressure is 7.5 MPa.

II. Comparison between API 602 and BS 1873 Standards

1. API 602 Standard

API 602 is a standard for small forged globe valves and is widely used in the petroleum, natural gas and chemical industries. This standard stipulates the design, manufacturing and testing requirements of globe valves to ensure the reliability and safety of the valves under high-pressure and high-temperature working conditions.

• Scope of Application: API 602 is applicable to globe valves with nominal diameters ranging from NPS 1/2 to NPS 2 (DN 15 to DN 50), and the pressure ratings include Class 150 to Class 2500.
• Material Selection: API 602 requires the use of high-strength carbon steel or alloy steel to manufacture the valve body and valve cover to ensure that the valve can withstand the high-pressure and high-temperature working environment.
• Design Features: API 602 emphasizes the structural strength and sealing performance of the valve and requires that the valve be designed to effectively prevent medium leakage.

2. BS 1873 Standard
BS 1873 is a standard for cast steel globe valves formulated by the British Standards Institution and is applicable to a variety of industrial applications. This standard imposes strict requirements on the materials, design and manufacturing processes of valves to ensure the safety and reliability of the valves under various working conditions.

• Scope of Application: BS 1873 is applicable to globe valves with nominal diameters ranging from DN 15 to DN 300, and the pressure ratings include PN16 to PN420.
• Material Selection: BS 1873 requires the use of high-quality cast steel materials to manufacture the valve body and valve cover to ensure the strength and durability of the valve.

• Design Features: BS 1873 emphasizes the sealing performance and operational flexibility of the valve and requires that the valve be designed to effectively prevent medium leakage and be convenient for operation and maintenance.

III. How to Select Globe Valves Using ASME B16.34 P-T Ratings

1. Determine Working Conditions

2. Select an Appropriate Pressure Rating

Based on the working conditions, refer to the P-T rating table of ASME B16.34 and select an appropriate pressure rating. For example, if the working pressure is 5.0 MPa and the working temperature is 200 °C, a Class 600 valve can be selected because its maximum allowable working pressure at this temperature can meet the requirements.

3. Consider the Impact of Temperature

In high-temperature working conditions, special attention needs to be paid to the impact of temperature on the pressure rating. ASME B16.34 provides detailed temperature-pressure curves to help you determine the actual working pressure of the valve at different temperatures. For example, the maximum allowable working pressure of a Class 600 valve at 200 °C may be lower than its pressure rating at room temperature.

4. Evaluate the Test Pressure

In addition to the working pressure, it is also necessary to evaluate the test pressure of the valve. The test pressure is usually 1.5 times the working pressure and is used to ensure the safety and reliability of the valve in actual use. For example, for a Class 600 valve, the maximum allowable working pressure at room temperature is 10.34 MPa, and its shell hydrostatic test pressure is 15.51 MPa.

5. Comprehensively Consider the Requirements of API 602 and BS 1873

When selecting a globe valve, it is also necessary to comprehensively consider the requirements of API 602 and BS 1873. API 602 pays more attention to the structural strength and sealing performance of the valve and is applicable to high-pressure and high-temperature working conditions, while BS 1873 emphasizes the sealing performance and operational flexibility of the valve and is applicable to a variety of industrial applications.

IV. Summary

The P-T ratings of ASME B16.34 provide an important reference basis for selecting and evaluating globe valves that comply with the API 602 and BS 1873 standards. When selecting a globe valve, it is necessary to comprehensively consider the working conditions, pressure ratings, the impact of temperature, test pressure, as well as the requirements of API 602 and BS 1873 to ensure the safety and reliability of the valve in actual use. through the introduction in this article, it is hoped that you can better understand and apply the p-t ratings of asme b16.34 and select the most suitable globe valve for your industrial applications.